Hydroprocess for a hydrocarbon stream from coal tar

ABSTRACT

A coal tar process is described. A coal tar stream is provided, and the coal tar stream is separated to provide a plurality of hydrocarbon streams. At least one of the hydrocarbon streams is hydroprocessed in a fluidized bed hydroprocessing zone with a catalyst to provide a gaseous volatile product and a solid heavy hydrocarbon product absorbed onto the catalyst. The gaseous volatile product is separated from the catalyst. The catalyst is regenerating by separating the absorbed heavy hydrocarbon product from the catalyst. The regenerated catalyst is recycled into the hydroprocessing zone.

This application claims the benefit of Provisional Application Ser. No. 61/905,988 filed Nov. 19, 2013, entitled Hydroprocess for a Hydrocarbon Stream from Coal Tar.

BACKGROUND OF THE INVENTION

Many different types of chemicals are produced from the processing of petroleum. However, petroleum is becoming more expensive because of increased demand in recent decades.

Therefore, attempts have been made to provide alternative sources for the starting materials for manufacturing chemicals. Attention is now being focused on producing liquid hydrocarbons from solid carbonaceous materials, such as coal, which is available in large quantities in countries such as the United States and China.

Pyrolysis of coal produces coke and coal tar. The coke-making or “coking” process consists of heating the material in closed vessels in the absence of oxygen to very high temperatures. Coke is a porous but hard residue that is mostly carbon and inorganic ash, which is used in making steel.

Coal tar is the volatile material that is driven off during heating, and it comprises a mixture of a number of hydrocarbon compounds. It can be separated to yield a variety of organic compounds, such as benzene, toluene, xylene, naphthalene, anthracene, and phenanthrene. These organic compounds can be used to make numerous products, for example, dyes, drugs, explosives, flavorings, perfumes, preservatives, synthetic resins, and paints and stains. The residual pitch left from the separation is used for paving, roofing, waterproofing, and insulation.

Coal tar hydrocarbon streams, especially heavier hydrocarbon streams and pitch, can be difficult to crack in hydroprocessing, resulting in an undesirable ratio of pitch to more valuable volatile products.

There is a need for an improved hydroprocessing method for coal tar streams.

SUMMARY OF THE INVENTION

One aspect of the invention involves a coal tar process. A coal tar stream is provided, and the coal tar stream is separated to provide a plurality of hydrocarbon streams. At least one of the hydrocarbon streams is hydroprocessed in a fluidized bed hydroprocessing zone with a catalyst to provide a gaseous volatile product and a solid heavy hydrocarbon product absorbed onto the catalyst. The gaseous volatile product is separated from the catalyst. The catalyst is regenerated by separating the absorbed heavy hydrocarbon product from the catalyst. The regenerated catalyst is recycled into the hydroprocessing zone.

Another aspect of the invention involves a coal tar process. A coal feed is pyrolyzed to provide a coal tar stream and a coke stream. The coal tar stream is separated to provide a plurality of hydrocarbon streams. At least one of the hydrocarbon streams is hydroprocessed in a fluidized bed hydroprocessing zone with a catalyst to provide a gaseous volatile product and a solid heavy hydrocarbon product absorbed onto the catalyst. The gaseous volatile product is separated from the catalyst, and the catalyst is regenerated by separating the absorbed heavy hydrocarbon product from the catalyst. The regenerated catalyst is recycled into the hydroprocessing zone.

Another aspect of the invention involves a coal tar process. A hydrocarbon stream from a coal tar stream is hydroprocessed in a fluidized bed hydroprocessing zone with a catalyst to provide a gaseous volatile product and a solid heavy hydrocarbon product absorbed onto the catalyst. The gaseous volatile product is separated from the catalyst, and the catalyst is regenerated by separating the absorbed heavy hydrocarbon product from the catalyst. The regenerated catalyst is recycled into the hydroprocessing zone.

BRIEF DESCRIPTION OF THE DRAWING

The Figure is an illustration of one embodiment of the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The Figure shows one embodiment of a process 5 of the present invention. A coal feed 10 can be sent to a pyrolysis zone 15 for pyrolyzing. In some example processes, a portion of the coal feed 10 is sent to a gasification zone (not shown), for instance the coal feed 10 can be split into two parts and sent to both.

In some processes, all or a portion of the coal feed 10 is mixed with oxygen and steam and reacted under heat and pressure in the gasification zone to form syngas, which is a mixture of carbon monoxide and hydrogen. The syngas can be further processed using the Fischer-Tropsch reaction to produce gasoline or using the water-gas shift reaction to produce more hydrogen.

In the pyrolysis zone 15, the coal is heated at high temperature, e.g., up to about 2,000° C. (3600° F.), in the absence of oxygen to drive off the volatile components. Coking produces a coke stream 20 and a coal tar stream 25. The coke stream 20 can be used in other processes, such as the manufacture of steel.

The coal tar stream 25 is sent to a fractionation zone 30 for separation. Coal tar comprises a complex mixture of heterocyclic aromatic compounds and their derivatives with a wide range of boiling points. The number of fractions and the components in the various fractions can be varied as is well known in the art. A typical separation process involves separating the coal tar stream 25 into four to six streams. For example, there can be a fraction 35 comprising NH₃, CO, and light hydrocarbons, a light oil fraction 40 with boiling points between 0° C. and 180° C., a middle oil fraction 45 with boiling points between 180° C. to 230° C., a heavy oil fraction 50 with boiling points between 230 to 270° C., an anthracene oil fraction with boiling points between 270° C. to 350° C., and pitch 55.

The light oil fraction contains compounds such as benzenes, toluenes, xylenes, naphtha, coumarone-indene, dicyclopentadiene, pyridine, and picolines. The middle oil fraction contains compounds such as phenols, cresols and cresylic acids, xylenols, naphthalene, high boiling tar acids, and high boiling tar bases. The heavy oil fraction contains creosotes, for example. The anthracene oil fraction contains anthracene. Pitch is the residue of the coal tar distillation containing primarily aromatic hydrocarbons and heterocyclic compounds.

Preferred processes hydroprocess coal tar streams that are difficult to crack; e.g. heavy coal tar streams. In an example embodiment, the fractionation zone 30 separates the coal tar stream into a fraction comprising NH₃, CO, and light hydrocarbons 35, light and middle oil fractions 40, 45, and at least one heavy oil fraction 50 having a minimum boiling point of about 450° C. to about 500° C. The heavy fraction 50 is introduced to a fluidized bed hydroprocessing zone 60, with hydrogen co-feed streams 57 and 58 including fresh hydrogen stream 56 and recycle stream 82, for hydroprocessing, e.g., hydrocracking, the heavy fraction 50.

The hydrocarbon stream that is input to the fluidized bed hydroprocessing zone 60 can come from other sources. The pitch stream 55 can be input to the hydroprocessing zone 60. In another example process, the fractionation zone 30 is replaced with a solvent extractor (not shown), which extracts a coal tar stream with a solvent such as toluene, hexane, tetrahydrofuran, or combinations thereof The solvent extractor outputs a toluene-insoluble stream, a hexane-insoluble stream, a tetrahydrofuran stream, or a combination. This output can be introduced to the hydroprocessing zone 60. In another example process, a heavy end coal tar stream taken directly from the pyrolysis zone 15, for example a coal tar stream having a minimum boiling point of at least 525° C., is input to the hydroprocessing zone without intermediate separation such as fractionation or solvent extraction. The coal tar stream can be obtained from sources other than pyrolyzing the coal feed 10 in the pyrolysis zone 15, and this coal tar stream can either be separated and fed to the hydroprocessing zone 60, or a heavy feed coal tar stream can be directly input into the hydroprocessing zone.

Hydrocracking is a process in which hydrocarbons crack in the presence of hydrogen to lower molecular weight hydrocarbons. Typical hydrocracking conditions may include a temperature of about 290° C. (550° F.) to about 468° C. (875° F.), a pressure of about 3.5 MPa (500 psig) to about 20.7 MPa (3000 psig), a liquid hourly space velocity (LHSV) of about 1.0 to less than about 2.5 hr⁻¹, and a hydrogen rate of about 421 to about 2,527 Nm³/m³ oil (2,500-15,000 scf/bbl). Typical hydrocracking catalysts include amorphous silica-alumina bases or low-level zeolite bases combined with one or more Group VIII or Group VIB metal hydrogenating components, or a crystalline zeolite cracking base upon which is deposited a Group VIII metal hydrogenating component. Additional hydrogenating components may be selected from Group VIB for incorporation with the zeolite base.

The example fluidized bed hydroprocessing zone 60 includes a plurality of zones for hydrocracking the hydrocarbon stream, e.g., heavy oil fraction 50. An outer, reaction zone 65 includes a fluidized bed having an active hydrocracking catalyst disposed therein. The catalyst preferably is powdered. Example active hydrocracking catalysts include non-noble metals. Preferred catalysts include Ni—Mo and W—Mo. The catalyst preferably is on a spray-dried alumina or silica-aluminum base. The catalyst is circulated internally through the hydroprocessing zone 60. An example fluidized bed hydroprocessing zone 60 includes one or more internal riser reactors 70 contained within an outer fluidized reactor 65. The heavy fraction 50 and hydrogen co-feed stream 57 are mixed to provide a combined hydrocarbon and hydrogen stream 59 which is divided and injected into the bottom of each of the internal riser reactors 70 with sufficient velocity to lift a portion of the catalyst within the fluidized bed 65 through the internal riser to thoroughly mix the hydrocarbon, hydrogen and catalyst and initiate the hydroprocessing reactions. The second hydrogen co-feed stream 58 is fed through a distributor to the bottom of the fluidized bed 65 to provide fluidization. At the top of the riser reactors 70 the majority of the catalyst and any adsorbed or liquid-phase hydrocarbon drop down into the fluidized bed 65 for further hydroprocessing.

During hydrocracking, hydrogen is provided at a very high pressure, e.g., an H₂ partial pressure ranging from about 3.4 MPa (500 psig) to about 17.2 MPa (2500 psig). An example temperature range is between about 350° C. to about 600° C. During hydrocracking, a gaseous volatile product is produced, as well as a solid heavy hydrocarbon product (e.g., pitch) that is absorbed on the catalyst. A feed rate and withdrawal rate of the hydrocarbon stream into and out of the hydroprocessing zone 60 can be controlled in relation to reaction activity to reduce the buildup of heavy material (i.e., the amount of absorbed pitch) on the catalyst. This limits buildup of solids on the catalyst and preferably keeps the catalyst in a powder form. A portion of the circulated catalyst with the adsorbed pitch is removed as a free-flowing solid 95 from the fluidized bed 65.

Any unconverted hydrogen and gas phase hydrocarbon from either the top of the internal riser reactors 70 or the top of the fluidized bed 65, as well as any entrained catalyst particles and hydrocarbon aerosol, exit the fluidized bed hydroprocessing zone 60 through a disengaging zone 75, preferably disposed internally to the reaction zone 60, to separate gaseous volatile products (gas phase) from the catalyst (solid phase) that includes non-volatile products. The disengaging zone 75 separates the gas and solid phase by the use of one or more stages of cyclone separators operating at about reactor temperature and pressure. The separated gaseous volatile product 80 is removed as an output of the disengaging zone 75 from the top of the hydroprocessing zone 60. The separated gaseous volatile product 80 cooled in a condenser 81 to give a gas-phase product stream 82 consisting primarily of unreacted hydrogen and a liquid-phase condensed hydrocarbon stream. A portion of the gas-phase product can be recycled back to the hydroprocessing reactor via lines 57 and 58, while the remainder is recovered as a vapor product 84. The condensed hydrocarbon stream 83 can be processed in a processing zone 85 to provide one or more products 90.

The separated catalyst 95 is then fed to a regeneration zone 100 for separating the absorbed heavy hydrocarbon product from the catalyst. The regeneration zone 100 preferably is a separate vessel from the hydroprocessing zone 60. In the regeneration zone 100, the absorbed heavy hydrocarbon product is burned off from the catalyst. For instance, the absorbed heavy hydrocarbon product can be burned at high temperatures, e.g., 450-800° C., with an air input 97.

Alternatively, the separated catalyst 95 can be regenerated by an extraction process such as solvent extraction using a solvent such as paraffins, aromatics, sulfolane, and other polar aprotic organic solvents at 100-250° C., a solvent to catalyst weight ratio of 1:1 to 100:1 and sufficient pressure to maintain the solvent in the liquid phase at the extraction temperature.

The burned off or otherwise separated heavy hydrocarbon product is output via stream 105. The regenerated, solid catalyst 110 is circulated to the fluidized bed 65.

Example processes for the condensed hydrocarbon stream 83 in the processing zone include hydrotreating, hydrocracking, deoxygenation, desulfurization, and hydrogenation. Hydrotreating is a process in which hydrogen gas is contacted with a hydrocarbon stream in the presence of suitable catalysts which are primarily active for the removal of heteroatoms, such as sulfur, nitrogen, and metals from the hydrocarbon feedstock. In hydrotreating, hydrocarbons with double and triple bonds may be saturated. Aromatics may also be saturated. Typical hydrotreating reaction conditions include a temperature of about 290° C. (550° F.) to about 455° C. (850° F.), a pressure of about 3.4 MPa (500 psig) to about 26.7 MPa (4000 psig), a liquid hourly space velocity of about 0.5 hr-1 to about 4 hr-I, and a hydrogen rate of about 168 to about 1,011 Nm3/m3 oil (1,000-6,000 scf/bbl). Typical hydrotreating catalysts include at least one Group VIII metal, preferably iron, cobalt and nickel, and at least one Group VI metal, preferably molybdenum and tungsten, on a high surface area support material, preferably alumina. Other typical hydrotreating catalysts include zeolitic catalysts, as well as noble metal catalysts where the noble metal is selected from palladium and platinum.

Hydrocracking is a process in which hydrocarbons crack in the presence of hydrogen to lower molecular weight hydrocarbons. Typical hydrocracking conditions may include a temperature of about 290° C. (550° F.) to about 468° C. (875° F.), a pressure of about 3.5 MPa (500 psig) to about 20.7 MPa (3000 psig), a liquid hourly space velocity (LHSV) of about 1.0 to less than about 2.5 hr⁻¹, and a hydrogen rate of about 421 to about 2,527 Nm³/m³ oil (2,500-15,000 scfibbl). Typical hydrocracking catalysts include amorphous silica-alumina bases or low-level zeolite bases combined with one or more Group VIII or Group VIB metal hydrogenating components, or a crystalline zeolite cracking base upon which is deposited a Group VIII metal hydrogenating component. Additional hydrogenating components may be selected from Group VIB for incorporation with the zeolite base.

Deoxygenation is a process for removing oxygen from a molecule. An example deoxygenation process hydroprocesses a feed by passing the feed to a hydrotreating unit where the feed is contacted with a hydrotreating catalyst. The hydrotreating unit can also be a hydrocracking unit with a hydrocracking catalyst. Hydrogenation and hydrotreating catalysts are also capable of catalyzing decarboxylation, decarbonylation, and/or hydrodeoxygenation of the feed to remove oxygen. Deoxygenation conditions include a relatively low pressure of about 1724 kPa absolute (250 psia) to about 10.342 kPa absolute (1500 psia), with embodiments in the range of 3447 kPa (500 psia) to about 6895 kPa (1000 psia) or below 4826 kPa (700 psia); a temperature of about 200° C. to about 460° C. with embodiments in the range of about 288° C. to about 345° C.; and a liquid hourly space velocity (LHSV) of about 0.25 to about 4 hr ⁻¹ with example embodiments in the range of about 1 to about 4 hr⁻¹. Since hydrogenation is an exothermic reaction, as the feedstock flows through a catalyst bed the temperature increases and decarboxylation, decarbonylation, and hydrodeoxygenation can occur. Although the hydrogenation reaction is exothermic, some feedstocks may be highly saturated and not generate enough heat internally. Therefore, some embodiments may require external heat input. All the reactions may occur simultaneously in one reactor or in one bed. Alternatively, the conditions can be controlled such that hydrogenation primarily occurs in one bed and decarboxylation, decarbonylation, and/or hydrodeoxygenation occurs in a second or additional bed(s). If only one bed is used, it may be operated so that hydrogenation occurs primarily at the front of the bed, while decarboxylation, decarbonylation and hydrodeoxygenation occur mainly in the middle and bottom of the bed. Hydrogenation can be carried out in one reactor, while decarboxylation, decarbonylation, and/or hydrodeoxygenation can be carried out in a separate reactor. However, the order of the reactions is not critical.

Desulfurization is a process for reducing sulfur of hydrocarbon feedstocks to lower levels. Desulfurization is typically performed by contacting a hydrocarbon feedstock in a desulfurization reaction vessel or zone with a suitable desulfurization catalyst under conditions of elevated temperature and pressure in the presence of hydrogen to yield a product containing the desired maximum limits of sulfur. An example hydrocarbon desulfurization process is disclosed in U.S. Pat. No. 7,108,779.

Suitable desulfurization catalysts include hydrotreating catalysts and include those which are comprised of at least one Group VIII metal, preferably iron, cobalt and nickel, more preferably cobalt and/or nickel and at least one Group VI metal, preferably molybdenum and tungsten, on a high surface area support material, preferably alumina. Other suitable desulfurization catalysts include zeolitic catalysts, as well as noble metal catalysts where the noble metal is selected from palladium and platinum. More than one type of desulfurization catalyst can be used in the same reaction vessel. The Group VIII metal is typically present in an amount ranging from about 2 to about 20 weight percent, preferably from about 4 to about 12 weight percent. The Group VI metal will typically be present in an amount ranging from about 1 to about 25 weight percent, preferably from about 2 to about 25 weight percent. Typical desulfurization temperatures range from about 204° C. (400° F.) to about 482° C. (900° F.) with pressures from about 2.1 MPa (300 psig) to about 17.3 MPa (2500 psig), preferably from about 2.1 MPa (300 psig) to about 13.9 MPa (2000 psig). Operating conditions and desulfurization catalysts within the desulfurization reactor can be selected to affect the quality of the desulfurized products.

Hydrogenation involves the addition of hydrogen to hydrogenatable hydrocarbon compounds. Alternatively hydrogen can be provided in a hydrogen-containing compound with ready available hydrogen, such as tetralin, alcohols, hydrogenated naphthalenes, and others via a transfer hydrogenation process with or without a catalyst. The hydrogenatable hydrocarbon compounds are introduced into a hydrogenation zone and contacted with a hydrogen-rich gaseous phase and a hydrogenation catalyst in order to hydrogenate at least a portion of the hydrogenatable hydrocarbon compounds. The catalytic hydrogenation zone may contain a fixed, ebulated or fluidized catalyst bed. This reaction zone is typically at a pressure from about 689 kPa gauge (100 psig) to about 13790 kPa gauge (2000 psig) with a maximum catalyst bed temperature in the range of about 177° C. (350° F.) to about 454° C. (850° F.). The liquid hourly space velocity is typically in the range from about 0.2 hr⁻¹ to about 10 hr⁻¹ and hydrogen circulation rates from about 200 standard cubic feet per barrel (SCFB) (35.6 m³/m³) to about 10,000 SCFB (1778 m³/m³).

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims. 

What is claimed is:
 1. A process comprising: providing a coal tar stream; separating the coal tar stream to provide a plurality of hydrocarbon streams; hydroprocessing at least one of the hydrocarbon streams in a fluidized bed hydroprocessing zone with a catalyst to provide a gaseous volatile product and a solid heavy hydrocarbon product absorbed onto the catalyst; separating the gaseous volatile product from the catalyst; regenerating the catalyst by separating the absorbed heavy hydrocarbon product from the catalyst; and recycling the regenerated catalyst into the hydroprocessing zone.
 2. The process of claim 1 wherein the hydrocarbon stream has a minimum boiling point of about 450° C. to about 500° C.
 3. The process of claim 1 wherein the hydrocarbon stream comprises one or more of a toluene-insoluble stream, a hexane-insoluble stream, and a tetrahydrofuran-insoluble stream.
 4. The process of claim 1 wherein the hydrocarbon stream comprises a pitch stream.
 5. The process of claim 1 wherein the hydroprocessing takes place at an H₂ partial pressure ranging from about 3.4 MPa (500 psig) to about 17.2 MPa (2500 psig).
 6. The process of claim 1 wherein regenerating the catalyst comprises burning off the absorbed heavy hydrocarbon product from the catalyst.
 7. The process of claim 1 wherein a hydrocarbon stream flow rate into the hydroprocessing zone is controlled based on a rate of catalyst withdrawal to reduce buildup of heavy material on the catalyst.
 8. The process of claim 1 further comprising: removing the separated gaseous volatile product.
 9. The process of claim 8 further comprising: processing the separated gaseous volatile product by one or more of hydrotreating, hydrocracking, catalytic cracking, deoxygenation, desulfurization, and hydrogenation.
 10. A process comprising: pyrolyzing a coal feed to provide a coal tar stream and a coke stream; separating the coal tar stream to provide a plurality of hydrocarbon streams; hydroprocessing at least one of the hydrocarbon streams in a fluidized bed hydroprocessing zone with a catalyst to provide a gaseous volatile product and a solid heavy hydrocarbon product absorbed onto the catalyst; separating the gaseous volatile product from the catalyst; regenerating the catalyst by separating the absorbed heavy hydrocarbon product from the catalyst; and recycling the regenerated catalyst into the hydroprocessing zone.
 11. The process of claim 10 wherein the hydrocarbon stream has a minimum boiling point of about 450° C. to about 500° C.
 12. The process of claim 10 wherein the hydrocarbon stream comprises a pitch stream.
 13. The process of claim 10 wherein the hydrocarbon stream comprises one or more of a toluene-insoluble stream, a hexane-insoluble stream, and a tetrahydrofuran-insoluble stream.
 14. The process of claim 10 wherein the hydroprocessing takes place at an H₂ partial pressure ranging from about 3.4 MPa (500 psig) to about 17.2 MPa (2500 psig).
 15. The process of claim 10 further comprising: removing the separated gaseous volatile product.
 16. The process of claim 15 further comprising: processing the separated gaseous volatile product by one or more of hydrotreating, hydrocracking, catalytic cracking, deoxygenation, desulfurization, and hydrogenation.
 17. A process comprising: hydroprocessing a hydrocarbon stream from a coal tar stream in a fluidized bed hydroprocessing zone with a catalyst to provide a gaseous volatile product and a solid heavy hydrocarbon product absorbed onto the catalyst; separating the gaseous volatile product from the catalyst; regenerating the catalyst by separating the absorbed heavy hydrocarbon product from the catalyst; and recycling the regenerated catalyst into the hydroprocessing zone.
 18. The process of claim 17 wherein the hydrocarbon stream comprises one or more of a toluene-insoluble stream, a hexane-insoluble stream, and a tetrahydrofuran-insoluble stream.
 19. The process of claim 17 wherein the hydrocarbon stream comprises pitch.
 20. The process of claim 17 wherein the hydrocarbon stream comprises a coal stream having a minimum boiling point of at least 525° C. 